Electrical amplifier circuits



Nov. 4, 1930. s. Yfwl-uTE ELECTRICAL AMPLIFIER CIRCUITS Filed Aug. ll, 1925 v Patented Nov. 4, 1930 UNITED STATES PATENT OFFICE SIDNEY Y. WHITE, OF NEW YORK, Y., ASSIGNOR, BY MESNE ASSIGNMENTS, TO RADIO CORPORATION OF AMERICA, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE ELECTRICAL AMPLIFIER CIRCUITS Application led August 11, 1925. Serial No. 49,521.

While my invention relates generally to electrical amplier circuits, it refers particularly to means for tran-sferring alternating currents from the output circuit of one amplier into the input circuit of a succeeding amplifier. It is of particular advantage in connection with three electrode vacuum tube amplifiers in so-called cascade or tandem combinations, particularly in radio receivers employing cascaded three electrode vacuum tubes as amplifiers in the high frequency portion of such receivers.

An object of my invention is to provide a coupling means for energy transfer from one amplifier to another, in which the rate of energy transfer maybe cau-sed to vary in any manner desired with variationof -frequency of the currents being handled by the amplifiers. A particular object is to maintain the rate of energy transfer constant over a Wide `range of frequencies.

' Another object of my invention is an arrangement in the coupling which will prevent the direct current energizing otentials necessary for rendering the amplihers operative from being impressed upon other than the desired amplifier electrodeswhile employing common sources of such potentials for a plurality of amplifiers.` v f A furtherfobj ect of my invention is to limit andcontrolthe reaction of the output circuit oflan amplifier upon its input circuit which A circuit-s.

In a co-pending appllcation Serialv No.

`' reaction to take place.

accompanies resonant Aabstraction of energy from the output circuit where the inherent capacity path in such amplifiers permits such It is an object of my invention to provide a vcoupling Whose constancy or predetermined variation with frequency is automatically kand electrically provided for, and is simply er and readily applied to existing ampli 48,936, filed Augustv'?, 1925, I have described andk illustrated diagrammatically an electrical 'coupling means with which energy transfer may be made to remain constant with variation of frequency or may be caused to vary in a predetermined manner with variation of frequency, the description referringV to electrical circuits in general. I have discovered that the coupling means so described may, withY proper arrangements, be applied to amplifier circuits with many advanta eous results, particularly in the case of t reeelectrode vacuum tube amplifiers.

My present invention Will be best understood by reference to the figure in the accompanying drawing in which m invention is shown employed in the high requency portion lof 'a radio receiver having two threeelectrode vacuum tubes in this portion. The element X represents an antenna or collector circuit completed to ground Gr through a condenser C3 and an inductance element L1,

and may or may not include a condenser Cl,

depending upon Whether or not the physical characteristics of the antenna make suchv a condenser desirable.` A tunable absorbing circuit, including an inductance element L2, a variable condenser C2 and the ycondenser C3, -is coupled to the antennacircuit through the connection of the antenna around the l condenser C3, and through having the inductance element L1 and the-inductance yelement L2 inductively related. As more fullyl tion of coils L1 and L2 increases with increase of frequency.v Thus, with the polarity of the inductive' coupling chosen such that the currentspin 'the absorbing circuit due to electrostatic'ally v,and electromagnetically transferred energy are in phase oraiding, the decrease of transfer with frequency of increase of the other. The degree with which the transfer through the electrostatic coupling changes With frequency can be readily 5 controlled through appropriate choice of the relative capacity values of the coupling condenser C3 and the variable tuning condenser C2, vsince coupling is a function not only of the capacity common to the tvvo circuits, but involves the non-common capacity as Well. Thus the electro-static coupling may be caused to varycin a pre-determined Way with frequency, and combined with the electromagnetic coupling give a resultant coupling to transfer energy predetermined to either increase or decrease with frequency increase, or to remain constant with frequency change.

The absorbing circuit is shown as the input circuit to the three-electrode vacuum tube amplifier VTI, and as tunable for selective absorption from the antenna circuit through variation of the condenser C2.-

Thev output circuit of the vacuum tube VTI is shown as including an inductance 'JelementLl and a condenser element C3 as in the case of the antenna circuit just previously described. An absorption circuit, including the inductance element Lz, variable condenser Clz and condenser Cs, which is the input circuit of a second vacuum tube VT2, is shown associated With the output circuit in the manner described for the association of the absorption circuit to the antenna circuit and may, through like adjustments described with respect to the coupling for the former circuits, be made to transfer energy at a rate remaining constant with frequency or varying in any predetermined manner. Vacuum tube VTl is illustrated as connected for straight amplification work through having its grid return lead connected to the negative side of the `filament ener-4 gizing source. Vacuum tube VT2 is shown as connected for detection work through havingvthe well-known gridleak-stopping condenser combination GL, and having its grid return connected to the positive'Y side of the source for energizing the filament. The transformer T in the output circuit of vacum tube VT2 passes the detected currents n to an audio frequency amplifier or direct to a translating device.

The Wires to terminals marked +A-B,

A, and +B, indicate the usual connections for energizing from batteries or other suitable energy sources the output circuits andl the filaments of thevacuum tubes and are thought to require no descriptionI in detail.

In view of the condenser C3 interrupting the output circuit of vacuum tube VTI for direct current flow, it is necessary to provide a shunt path around this condenser, which is shown as the path including the inductance element L3. In order to compel the amplilied -alternating currents to seek 'the path containing the condenser C3, it is necessary to provide the inductance L3 with suiiicient impedance to accomplish the result. In radio frequency Work such a device is commonly termed a radio frequency choke, and is well known to the art. The main alternating current path is therefore from the plate ,of tube VTl through coil L1L and condenser Cs to the filament system, and in takingthis path transfers energy to the tunable input circuit of tube VT2 both electromagnetically and electrostatically in the manner hereinbefore described and subject to the adjustments described.

It will be seen that the condenser C2 acts to prevent positive high potential impressed upon the plate of vacuum tube VTI from reaching the grid of vacuum tube VT2. At

the same time the arrangement does not prevent properly biasing the grid of vacuum tube VT2 with respect to its filament. It will be seen that the positive potential, due to connecting the grid return of vacuum tube VT2 to the positive side of the filament energizing source, reaches the grid through the conductive path provided by the inductance L2 and the gridleak resistance.

It is Well known in vacuum tube practice that the inherent capacity between the elements in the tube, particularly between the grid and plate elements, is a disturbing factor of no little moment, particularly in high frequency Work, the disturbance arising through this capacity providing a path through which the amplified energy in the plate circuit can in part flow to the grid circuit to augment, when in correct phase, the grid circuit energy, often resulting in the system becoming a generator of oscillations. The amount of energy which escapes to the grid circuit depends upon the extent of reaction of the plate circuit on the amplified energy, or in other words, the counter electromotive force set up in the plate circuit, and the affect of this plate-circuit-originated energy upon the, action of the tube depends upon its phase relation with respect to the original energy in the grid circuit. The reaction of the plate circuit upon the energy and the phase relations depend upon the reactance characteristics of the plate circuit. tendency to oscillate is maximum when the output circuit, during the process of tuning,

-Within the range of frequencies for which the receiver is designed, and therefore no oscillation produclng reaction results from this circuit alone. On the other hand, I abstract The disturbing' energy from the output circuit into the absorbing circuit forming the input circuit of the succeeding vacuum tube, and this abstraction of energy produces a greater reaction than is had due to the plate circuit alone,

as Well as varies the nature of the reaction from inductive to capacitive and viceversa as the absorbing circuit may be tuned from one side to the other of resonance in carrying out the tuning adjustments. The degree of reaction, however, will depend upon the degree of coupling between the two circuits. When I desire to keep the reaction suiiiciently low to prevent the system from oscillating, I make the coupling between the two circuits loose, preferably by makin the number of turns in the coil Ll small with respect to the number of turns on the coil Le, and the value of the condenser C8 large with respect to the value of the `condenser C2. With the coupling made sufficiently loose, and the constants involved in the coupling adjusted so that the rate of energy transfer remains constant throughouta wide range of frequencies, as heretofore described, I am enabled to continuously tune the absorbing circuit in the input circuit of vacuum tube VT2 in consonance with the input circuit of vacuum tube VTl without throwing the system into oscillations, and at the same time obtaina most eiicient transfer of energy throughout the desired range of frequencies. j It will be appreciated that this control over the reaction is electrically automatic. In the ordinary inductive form of coupling, if the coupling is made sufficiently loose not to have oscillations at the higher frequencies of a desired band, itl becomes inefficient in energy transfer at the lower frequencies of the band.

It will be seen that my system is extremely simple and inexpensive, requiring forordinary radio practice the addition of an inexpensive fixed condenser CS and an inexpensive radio frequency choke L3, and the use of these elements will in many systems, permit the removal of other elements used for preventing oscillations.

` While I have described and illustrated my invention in connection with its use in a radio receiver, many other applications will be readily apparent to those`skilled in the art, and I do not wish to be limited in its scope to the chosen system for descriptive purposes.

Having fully described my invention, I claim:

l. An electrical system composed of an amplier of alternating currents, a tunable input circuit, an output circuit, an internal path in said ampliiier connecting said output circuit to said input circuit, a tunable absorbing circuit associated with said output circuit, and means for limiting ampliied energy feed-back through said internal path comprising means for loosely coupling` said ab- 2. An electrical amplifying system including a three electrode vacuum tube, an adjustable period circuit connected to the input electrodes of said tube, an output circuit, a responslve device, and means for controlling the reaction of said output circuit and ab- 75 straction of energy therefrom for said responsive device over a wide range of frequencies that a predetermined effect in said responsive device with frequency is obtained, includinga circuit coupled to said SO output circuit adapted to be adjusted in period in consonance with said adjustable period input circuit, and across which second adjustable circuit said responsive device is connected, said 4coupling including a pair of S5 coupling elements transferringA energy in phase, one of which couplings increases in effect with frequency increase and the other of which couplings decreases in effect with frequency increase, the relative Values of said couplings being chosen to give the said predetermined e'ect over a wide range of frei Y quencies.

3. In an electrical system including a three electrode vacuum tube, a selectively variable 9,-, input clrcuit and an output circuit, said tube o having internal capacity through which `ampliiied energy may be regeneratively transferred from said output circuit to said input circuit in degree dependent upon the value of 10d said capacity, frequency of current energy, and potential of reaction to current flow in said output circuit, the method of controlling the regenerative conduct of said system from frequency to frequency as said variable input circuit is varied which consists of selectively absorbing energy both electrostatically and electromagnetically in phase from said output circuit in consonance with the varying of said input circuit at a rate to produce an absorption reaction on said output circuit to cause a desired order of regeneration through said tube capacity, controlling said selective absorption electrostatically whereby said electromagnetic absorption decreases 115 with frequency decrease, and so relating the Variation of'electrostatic absorption to the necessary electrostatic variation for selective absorption that said electrostatic absorption increases withy frequency decrease at such rate that the regeneration remains substan- 'tially constant with frequency change.

4. In an electrical system including a three electrode vacuum tube, a selectively variable input circuit and an output circuit, said tube having internal capacity through which ampliied energy may be regeneratively transferred from said output circuit to said input circuit in degree dependent upon the value of said capacity, frequency of current energy,

and potential of reaction to currentliow in said output circuit, the method of controlllng the regenerative conduct of said system from `frequency to frequency as said variable input circuit is varied which consists of selectively absorbing energy from said output circuit in consonance with the varying of said input circuit at a rate to produce an absorption reaction'on said output circuit to cause a way.

5. In an electrical system including a three electrode vacuum tube, a selectively variable input circuit and 'an output circuit, said tube having internal capacity through which amplified energy may be regeneratively transferred from said output circuit to said input circuit in degree dependent upon the value of said capacity, frequency of current energy, and the potential of reaction to current flow in said output circuit, the method of controlling the regenerative conduct of said system from frequency to frequency as said variable input circuit is varied which consists of selectively absorbing energy from said output circuit in consonance with the varying of said input circuit at a rate to produce an absorption reaction on said output circuit of potential to cause a desired degree of regeneration through said tube capacity, and controlling said rate of selective absorption from said output circuit from frequency to frequency to produce reactions on said output circuit which, combining with other reactions of said output circuit, cause a desired,frequency-to-frequency character of regeneration.

6. In an electrical system including a source of alternating currents of a wide range of frequencies, the electrical conduct of said source towards currents of different frequencies depending upon the nature of the reactions to said currents of different frequencies of a circuit connected to the output terminals thereof, the method of controlling said reactions with frequency as the current output of said source is changed from frequency to frequency which consists of selectively absorbing energy both electrostatically and electromagnetically in phase from said output circuit in frequency consonance with the currents therein to selectively create absorption reaction thereon, controlling said selective absorption electrostatically whereby said electromagnetic absorption decreases with frequency decrease, and so relating the variation of electrostatic absorption to the necessary electrostatic variation for selective absorption that said electrostatic absorption increases with frequency decrease at such rate that the effect of said electromagnetic absorption on the reactions of said output circuit with frequency is modified Yin a desired way.

7. In an electrical system including a source of alternating currents of a wide range of frequencies, the electrical conduct of said source towards currents of different frequencies depending upon the nature of the reactions to said currents of different frequencies of a circuit connected to the outvput terminals thereof, the method of controlling said reactions with frequency as the current output of said source is changed from frequency to frequency which consists of selectively absorbing energy from said output circuit by way of a coupling which transfers energy increasingly with frequency increase in frequency consonance with the currents therein to selectively create absorption reaction thereon, furtherV simultaneously selectively absorbing energy from said output in phase with said first selective absorp tion by way of a coupling which transfers energy decreasingly with frequency increase, and selecting the rate of change of energy transfer with frequency of one of said couplings to produce a predetermined character with frequency of combined absorption reac# tion on said out-put circuit whereby the conduct of said source with frequency is controlled in a desired way.

8. In a selective current amplifying and relaying system including a three electrode vacuum tube having internal capacity, a selectively variable input circuit, an output circuit, a second circuit selectively variable by capacity variation in consonance with said input circuit coupled to said output circuit` and a responsive device connected across said second variable circuit, whereby the amplifying and relaying to said responsive device varies with frequency b reason of a resultant of variation with requency of the effect of said internal capacity of said tube, the reaction of the elements in said output circuit through said internal capacity, the usual inconstant reaction of said capacitively variable second circuit on said output circuit, and the usual inconstant transfer of energy from said output circuit to said second variable circuit, the method of maintaining the level of amplified energy delivery to said responsive device substantially constant from frequency to frequency as said vvariable circuits are varied, which consists of transferring the energy from said output circuit to said second variable circuit through a pair of couplings acting in phase, and controlling the rate of change of energy transfer with frequency through one of said couplings to produce varying effects with frequency in reaction on said output circuit and energy transfer therefrom which in combination form a resultant effect at said responsive. device having a frequency characteristic substantially the reverse of that vof the resultant of said Varying effects.

9. In an electrical system the combination of a three electrode vacuum tube having inherent capacity between its electrodes, a selectively variable input circuit, an output circuit, and means for 'controlling the regenerative conduct of said system from frequency to frequency as said input circuit is Varied comprising a circuit variable in consonance with sai-d input circuit, and a pair bf couplings between said output circuit and said second Variable circuit transferring energy therebetween in aiding phase to produce a Acombined absorption reaction on said output lcircuit, one of said couplings transferring energy increasingly with increase of frequency, and the other of said couplings transferring energy decreasingly with increase of frequency, the rate of transfer of said second coupling from frequency to frequency being governed by a predetermined relation between said coupling element and a variable element in said second `variable circuit.

10. In an electrical system the combination of a source of alternating currents of a wide f vrange of frequencies, an output circuit, the

electrical conduct of said source towards currents of 'different frequencies depending upon the nature of the reactions of said output circuit to said currents, and means for controlling the electrical conduct of said source from frequency to frequency through control of said reactions comprising a circuit variablein period over said wide range of frequencies coupled to said output circuit through a coupling which changes the absorption reaction of said variable circuit on sai-d output circuit as varied from frequency to frequency, and a s`econd coupling between said circuits in phase accord with said first coupling, said second coupling being adapted to change the absorption reaction of said Variable circuit on said output circuit from frequency to frequency inversely to the change y produced by said first coupling.

11. In an electrical system the combination of a'source'of .alternating currents of a wide range of frequencies, an output circuit, and means for maintaining the relation of the internal impedance of said source to the output impedance substantially constant from frequency to frequency of selected current output from said source comprising a circuit variable in period over said wide range of frequencies coupled to said output circuit through a pair of couplings in phase quency to frequency to that of said first couv 12. In an electrical system the combination of a three electrode vacuum tube having inherent capacity between its electrodes, a selectively variable input circuit, an output circuit, and means for controlling the regenerative conduct of said system from frequency to frequency as said input circuit is Varied comprising a circuit electrostatically variable in consonance with said input circuit, an electromagnetic couplinghbetween .said output circuit and said second variable circuit, and an electrostatic coupling between said circuits in phase accord with said electromagnetic coupling, said electrostatic coupling having such dependency upon the value of the variable electrostatic element in said second variable circuit that the varying of said element produces a desired characteristic of electrostatic energy transfer with frequency which combines with the uncontrolled electromagnetic energy transfer character'- istic to produce a resultant characteristic representing a desired reaction on said output circuit `whereby regeneration is controlled in a desired way with frequency. l

13. In a selective radio frequency amplifying system the combination of a three electrode vacuum tube having inherent capacity between its electrodes, a variable period input circuit, an output circuit, a second variable period circuit, a second vacuum tube aconnected directly across said second variable circuit, and means for maintaining the amplified energy level selectively delivered to said second tube substantially constant from frequency to frequency as said variablecircuits are adjusted in substantial consonance while preventing oscillation production ent upon the value of the variable tuning element of said second variable circuit that selection of therelative values of the coupling element and the tuning element permits of producing a coupling-frequency characteristie that combines with the characteristic of said rst coupling to produce a regenerative reaction and an energy transfer which combine to maintain a substantially constant energy delivery to said second vacuum tube.

In testimony whereof I affix my signature.

SIDNEY Y. W'HITE. 

